V2g system and charge/discharge control method

ABSTRACT

A V2G system includes: a power system; a charging/discharging device including an electricity storage unit, a power conversion unit that converts power transferred between the electricity storage unit and the power system, a reception unit, and a control unit that controls an operation of the power conversion unit based on a received signal; and a server device that manages charging and discharging of the electricity storage unit. The server device determines a period of time during which power is discharged from the electricity storage unit to the power system or during which the electricity storage unit is charged using power supplied from the power system, and transmits an instruction including the period of time to the charging/discharging device. The control unit of the charging/discharging device starts up or stop based on the period of time indicated by the instruction from the server device.

TECHNICAL FIELD

The present invention relates to a V2G system and a charge/dischargecontrol method regarding V2G (vehicle to grid) capable of bidirectionalpower transfer between electricity storage units provided in transportequipments and a power system.

BACKGROUND ART

Patent literature 1 discloses a charging system for a vehicle having atiming function so that charging can be reserved, in which even thoughthe timing function is abnormal, charging can be started at a reservedcharging start time as much as possible. In the charging system for avehicle, upon occurrence of abnormality in the timing function of atiming function section, a control section determines whether start-upcan be continued in a normal mode until the charging start time based onthe residual power of a 12 V battery and its own power consumption. Whenit is determined that the start-up can be continued, the charging starttime is waited in the normal mode.

Patent literature 2 discloses a load leveling system in which eachbattery of a plurality of vehicles is charged during non-peak powerdemand at a business place, which is a power consumer receiving electricpower supplied from a power supply company, or by using midnight powerof each vehicle owner, and the electric power stored in the chargedvehicle battery is discharged during peak power demand at a businessplace.

PRIOR ART LITERATURE Patent Literature

-   Patent Literature 1: JP-A-2013-243791-   Patent Literature 2: JP-A-2007-282383-   Patent Literature 3: Japanese Patent No. 4285578

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

According to the charging system for a vehicle disclosed in Patentliterature 1, even though abnormality occurs in the timing function ofthe timing function section, since the control section continuesstart-up in the normal mode until the charging start time, it ispossible to start charging of a high voltage battery by determining thatthe charging start time is reached. However, in the charging system fora vehicle, since discharge from the high voltage battery installed atthe vehicle to an external power supply side is not performed, it is notpossible to apply the charging system for a vehicle of Patent literature1 to a V2G (Vehicle-to-Grid) system in which bidirectional powerexchange is possible between a power system including a commercial powernetwork and an electric vehicle such as EV (Electric Vehicle) and PHEV(Plug-in Hybrid Electric Vehicle), so that it is not possible tocontribute to stabilization of a commercial power system.

In the load leveling system disclosed in Patent literature 2, power issupplied to a business place from a battery of a vehicle parked at aparking lot during the daytime so as to perform load leveling, so thatthe battery of the vehicle contributed to the load leveling is chargedat the business place in the next morning or is charged using midnightpower at home. When a vehicle using the system reaches the businessplace, a battery installed at the vehicle is connected to one of parkinglot socket groups via a bidirectional charger. At the time point atwhich the battery is connected to the socket, the vehicle is in astandby mode in which no charge and discharge are performed. However, atthe time point at which power demand becomes large at the businessplace, an instruction is sent to the vehicle such that the standby modeis shifted to a discharge mode, and at the time point at which powerdemand becomes small, an instruction is sent to the vehicle such thatthe discharge mode is shifted to the standby mode. However, the loadleveling system performs load leveling by exchanging power between thebusiness place and the vehicle and performs no load leveling in a powersystem including a commercial power network. Therefore, since it is notpossible to increase the number of vehicles participating in V2G and theagreement probability of power trading between a power supplier and apower consumer, it is not possible to contribute to stabilization of acommercial power system. An object of the present invention is toprovide a charging/discharging device and a charge/discharge controlmethod, capable of contributing to the stabilization of a power system.

Means for Solving the Problem

With a view to achieving the object, Claim 1 defines a V2G systemincluding:

a power system;

a charging/discharging device including an electricity storage unit(e.g., a main battery 104 in an embodiment described below) that isprovided in a transport equipment (e.g., an electrically driventransport equipment 15 in the embodiment described below), a powerconversion unit (e.g., a bidirectional charger 103 in the embodimentdescribed below) that converts power transferred between the electricitystorage unit and the power system, a reception unit (e.g., a digitalcommunication portion 102 in the embodiment described below) thatreceives a signal from an external device, and a control unit (e.g., acharging and discharging ECU 107 in the embodiment described below) thatcontrols an operation of the power conversion unit based on the signalreceived by the reception unit; and

a server device (e.g., an aggregator 17 in the embodiment describedbelow) that manages charging and discharging of the electricity storageunit in the charging/discharging device,

in which the server device performs a time-series analysis on an amountof power supplied from a power supplier to the power system and anamount of power supplied from the power system to a power consumer,determines a period of time during which power is discharged from theelectricity storage unit of the charging/discharging device to the powersystem or during which the electricity storage unit is charged usingpower supplied from the power system based on a result of estimating apower supply-demand state of the power system and a minimum trading unitof an amount of power managed by the server device during power transferwith the power system, and transmits an instruction including the periodof time during which the discharging or the charging is performed to thecharging/discharging device, and

the control unit of the charging/discharging device starts up or stopsbased on the period of time indicated by the instruction that istransmitted from the server device and is received by the receptionunit.

Claim 2 defines, based on Claim 1, the V2G system, wherein

in which the server device determines a period of time during which thedischarging or the charging of the charging/discharging device isperformed based on the result of estimating the power supply-demandstate, the minimum trading unit of the amount of power managed duringpower transfer with the power system, and a total amount of powersecured for selling to the power system.

Claim 3 defines, based on Claim 1 or 2, the V2G system, wherein

in which the server device determines a period of time during which thecharging of the charging/discharging device is performed based on theresult of estimating the power supply-demand state, degree ofcontribution of the charging/discharging device to the power system, anda charge appropriateness level of a time slot in which the electricitystorage unit is charged such that, as the degree of contributionincreases, the electricity storage unit is charged in a time slot havinga higher charge appropriateness level, the charge appropriateness levelbeing calculated from an influence on deterioration of the electricitystorage unit.

Claim 4 defines, based on any one of Claims 1 to 3, the V2G system,wherein

in which in a case where an amount of power stored in the electricitystorage unit is a predetermined amount or higher, the control unit ofthe charging/discharging device controls an operation of the powerconversion unit such that the discharging starts at a time, which isearlier by a predetermined period of time than a start time of thedischarging indicated by the instruction, and is performed until an endtime of the discharging indicated by the instruction, and

the server device manages degree of contribution of each of thecharging/discharging devices to the power system and sets thecontribution to be high for the charging/discharging device includingthe electricity storage unit which performs the discharging for a periodof time longer than the period of time during which the discharging isperformed indicated by the instruction.

Claim 5 defines, based on any one of Claims 1 to 3, the V2G system,wherein

in which in a case where a preset activeness of discharging from theelectricity storage unit to the power system is a predetermined value orhigher, the control unit controls an operation of the power conversionunit such that the discharging starts at a time, which is earlier by apredetermined period of time than a start time of the dischargingindicated by the instruction, and is performed until an end time of thedischarging indicated by the instruction, and

the server device manages degree of contribution of each of thecharging/discharging devices to the power system and sets thecontribution to be high for the charging/discharging device includingthe electricity storage unit which performs the discharging for a periodof time longer than the period of time during which the discharging isperformed indicated by the instruction.

Claim 6 defines, based on any one of Claims 1 to 3, the V2G system,wherein

in which in a case where an amount of power stored in the electricitystorage unit is a predetermined amount or higher, the control unitcontrols an operation of the power conversion unit such that thedischarging starts at a start time of the discharging indicated by theinstruction and is performed until a time which is later by apredetermined period of time than an end time of the dischargingindicated by the instruction, and

the server device manages degree of contribution of each of thecharging/discharging devices to the power system and sets thecontribution to be high for the charging/discharging device includingthe electricity storage unit which performs the discharging for a periodof time longer than the period of time during which the discharging isperformed indicated by the instruction.

Claim 7 defines, based on any one of Claims 1 to 3, the V2G system,wherein

in which in a case where a preset activeness of discharging from theelectricity storage unit to the power system is a predetermined value orhigher, the control unit of the charging/discharging device controls anoperation of the power conversion unit such that the discharging startsat a start time of the discharging indicated by the instruction and isperformed until a time which is later by a predetermined period of timethan an end time of the discharging indicated by the instruction, and

the server device manages degree of contribution of each of thecharging/discharging devices to the power system and sets thecontribution to be high for the charging/discharging device includingthe electricity storage unit which performs the discharging for a periodof time longer than the period of time during which the discharging isperformed indicated by the instruction.

Claim 8 defines a method of charging and discharging an electricitystorage unit (e.g., a main battery 104 in an embodiment described below)in a V2G system, the V2G system including a power system, acharging/discharging device, and a server device (e.g., an aggregator 17in the embodiment described below),

the charging/discharging device including the electricity storage unitthat is provided in a transport equipment (e.g., an electrically driventransport equipment 15 in the embodiment described below), a powerconversion unit (e.g., a bidirectional charger 103 in an embodimentdescribed below) that converts power transferred between the electricitystorage unit and the power system, a reception unit (e.g., a digitalcommunication portion 102 in the embodiment described below) thatreceives a signal from an external device, and a control unit (e.g., acharging and discharging ECU 107 in the embodiment described below) thatcontrols an operation of the power conversion unit based on the signalreceived by the reception unit,

the server device managing charging and discharging of the electricitystorage unit in the charging/discharging device, and

the method including:

causing the server device to perform a time-series analysis on an amountof power supplied from a power supplier to the power system and anamount of power supplied from the power system to a power consumer, todetermine a period of time during which power is discharged from theelectricity storage unit of the charging/discharging device to the powersystem or during which the electricity storage unit is charged usingpower supplied from the power system based on a result of estimating apower supply-demand state of the power system and a minimum trading unitof an amount of power managed by the server device during power transferwith the power system, and to transmit an instruction including theperiod of time during which the discharging or the charging is performedto the charging/discharging device; and

causing the control unit of the charging/discharging device to start upor stop based on the period of time indicated by the instruction that istransmitted from the server device and is received by the receptionunit.

Advantageous Effects of the Invention

According to Claims 1 to 8, the period of time during which theelectricity storage unit of the charging/discharging device performs thecharging and discharging is determined by the server device based on theresult of estimating the power supply-demand state, and thecharging/discharging device operates according to the instruction fromthe charging/discharging device. Therefore, by supplying power from thecharging/discharging device to the power system according to theinstruction from the server device in a time slot in which the amount ofpower supply is tight with respect to the amount of power demand, thestability of power supply from the power system to the power consumer isimproved. In addition, by charging the electricity storage unit of thecharging/discharging device in a time slot in which the amount of powersupply is surplus with respect to the amount of power demand, thestability of the power system is improved. In addition, by setting theincentive to be high in a case where charging and discharging isperformed according to the instruction from the server device, theprofit rate of the owner of the charging/discharging device increases.Further, the period of time during which the electricity storage unit ofthe charging/discharging device performs the charging and discharging isdetermined by the server device based on the minimum trading unit of theamount of power managed during power transfer with the power system, andthe charging/discharging device operates according to the instructionfrom the charging/discharging device. Accordingly, the agreementprobability of selling power from the charging/discharging device to theserver device, or the agreement probability of selling power from theserver device to the power system can be improved. Due to thisadvantageous effect, the active discharging of the charging/dischargingdevice can be encouraged, and the power system can be stabilized. Thisway, the benefits of four parties involved in V2G including the serverdevice, the owner of the charging/discharging device, an operator of thepower system, the power consumer can be maximized.

In addition, the control unit of the charging/discharging device may besuspended during a period of time other than the period of time duringwhich the charging and discharging is performed according to theinstruction from the server device and the wait time thereof. Therefore,the durability of the control unit can be secured. In addition, thepower consumption by the control unit can be reduced during a period oftime during which charged and discharged is not performed.

Further, the period of time in which charging and discharging isperformed indicated by the instruction from the server device isdetermined based on the result of estimating the power supply-demandstate, which is obtained by the time-series analysis of the amount ofpower, and the minimum trading unit of the amount of power which ismanaged by the server device. Therefore, the content of the instructionto the charging/discharging device can be determined based on the timeslot in which the amount of power supply is tight with respect to theamount of power demand and the time slot in which the amount of powersupply is surplus with respect to the amount of power demand.

According to Claim 2, the period of time during which thecharging/discharging device performs the discharging is determined basedon the result of estimating the power supply-demand state, the minimumtrading unit, which is used in a power trading market and generally hasa considerable value, and the total amount of power secured by theserver device for selling to the power system, It is difficult for theelectricity storage unit provided in the transport equipment to store alarge amount of power that fulfills the minimum trading unit, and thecharging/discharging device is not required to discharge a large amountof power. Therefore, the agreement probability of selling power from thecharging/discharging device to the server device is improved. Inaddition, the server device can sell power to the power system as muchas possible.

According to Claim 3, the aggregator 17 determines a period of timeduring which the charging of the charging/discharging device isperformed based on the contribution to the power system and the chargeappropriateness level such that, as the degree of contributionincreases, the electricity storage unit is charged in a time slot havinga higher charge appropriateness level. The charging/discharging devicehaving a high contribution is likely to be instructed to start thecharging in a time slot having a high charge appropriateness level.Therefore, the progress of deterioration of the electricity storage unitcan be delayed. In particular, in a time slot having a high chargeappropriateness level, the progress of deterioration of the electricitystorage unit can be made substantially zero. Due to this advantageouseffect, the owner of the charging/discharging device, which hesitates toparticipate in V2G due to a concern that the electricity storage unitmay deteriorate when participating in V2G, can be encouraged to activelyperform the discharging of the charging/discharging device.

According to any one of Claims 4 to 7, the contribution to the powersystem is set to be high for the charging/discharging device includingthe electricity storage unit which performs the discharging for a periodof time longer than that indicated by the instruction from the serverdevice. In a case where the contribution is set to be high, the profitrate of the owner of the charging/discharging device during chargingincreases. Therefore, the active discharging of the charging/dischargingdevice can be encouraged. In addition, by performing the discharging ina time slot in which the amount of power supply is tight with respect tothe amount of power demand, the stability of the power system isimproved. In addition, in the power transaction market of V2G,separately from an ordinary transaction market, a previous adjustmentmarket in which both the unit transaction time and the unit transactionamount are small is present. In a case where the discharging can beperformed for a period of time longer than that of dischargingdetermined by the determination portion, the charging/discharging devicecan sell power in the previous adjustment market, and the power systemcan be further stabilized. This way, the benefits of four partiesinvolved in V2G including the server device, the owner of thecharging/discharging device, an operator of the power system, the powerconsumer can be maximized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an entire configuration of a V2Gsystem.

FIG. 2 is a block diagram illustrating an external power supply and anelectric vehicle constituting a part of the V2G system illustrated inFIG. 1.

FIG. 3 is a block diagram illustrating an aggregator and a communicationnetwork constituting a part of the V2G system illustrated in FIG. 1.

FIG. 4 is a flowchart for explaining charge/discharge control of a mainbattery provided in an electric vehicle managed by the aggregator.

FIG. 5 is a diagram illustrating each change in output and SOC of a mainbattery provided in an electric vehicle accompanied with an example ofcharge/discharge (including the V2G) of the main battery.

FIG. 6 is a diagram illustrating each change in output and SOC of a mainbattery provided in an electric vehicle accompanied with another exampleof charge/discharge (including the V2G) of the main battery.

FIG. 7 is a diagram illustrating each change in output and SOC of a mainbattery provided in an electric vehicle accompanied with another exampleof charge/discharge (including the V2G) of the main battery.

FIG. 8 is a diagram illustrating a change in a demand and supply balanceof a power market and a temperature in a V2G participation time periodillustrated in FIG. 5 and a time period earlier to the V2G participationtime period.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be describedwith reference to the drawings.

V2G (Vehicle-to-Grid) is a system that performs power interchangebetween a power system including a commercial power network and anelectric vehicle and when the electric vehicle is not used as a movementmeans, an electricity storage unit installed at the electric vehicle isused as a power storage facility. Therefore, bidirectional powerexchange is performed between the electric vehicle participating in theV2G and the power system.

FIG. 1 is a diagram illustrating an entire configuration of the V2Gsystem. As illustrated in FIG. 1, the V2G system includes a powersystem, which includes a power station 11 for generating power by energyof thermal power, wind power, atomic power, sunlight and the like, apower transmission network 12 of power generated by a power supplierincluding the power station 11, and the like, a power consumer 13 thatreceives the supply of power in accordance with electricity demand, anexternal power supply 14 connected to the power transmission network 12via a power distribution facility (not illustrated), an electric vehicle15 such as EV (Electric Vehicle) and PHEV (Plug-in Hybrid ElectricVehicle) having a chargeable/dischargeable electricity storage unit, acommunication network 16, and an aggregator 17 that managescharge/discharge of the electricity storage unit of the electric vehicle15 via the external power supply 14 connected to the communicationnetwork 16. The aggregator 17 can manage charge/discharge of a pluralityof a power storage device including the electricity storage unit of theelectric vehicle 15, thereby satisfying the requirements of an electricpower company running the power station 11, a power transmission companyrunning the power transmission network 12, and the like.

FIG. 2 is a block diagram illustrating the external power supply 14 andthe electric vehicle 15 constituting a part of the V2G systemillustrated in FIG. 1. As illustrated in FIG. 2, the external powersupply 14 includes a connector 22 provided at a distal end of a cable 21and a digital communication unit 23. The electric vehicle 15 includes aninlet 101, a digital communication unit 102, a bidirectional charger103, a main battery 104, a converter (CONV) 105, a sub-battery 106, acharge/discharge ECU 107, a battery ECU 108, and a radio unit 109. Whenthe electric vehicle 15 participates in the V2G, the start-up state ofan electric component of the electric vehicle 15 lasts for hours due tocharge/discharge of the electricity storage unit of the electric vehicle15 or its standby. However, since the long-term continuation of thestart-up state of the electric component is not preferable in terms ofdurability, it is preferable to stop the electric component according tonecessity.

Hereinafter, each element of the external power supply 14 will bedescribed.

The connector 22 performs power exchange between the external powersupply 14 and the electric vehicle 15 in the state of being connected tothe inlet 101 of the electric vehicle 15. The digital communication unit23 is connected to the communication network 16 via a home gateway 18,and superimposes a signal obtained from the aggregator 17 onelectricity, which is exchanged between the external power supply 14 andthe electric vehicle 15, by using a power line communication technology.Therefore, a control signal from the aggregator 17 is sent to theelectric vehicle 15 if the connector 22 is being connected to the inlet101 of the electric vehicle 15.

Next, each element of the electric vehicle 15 will be described.

To the inlet 101, the connector 22 of the external power supply 14 isdetachable. The digital communication unit 102 receives the signalsuperimposed on the electricity from the external power supply 14 by thepower line communication (digital communication) technology in the statein which the connector 22 of the external power supply 14 is mounted atthe inlet 101, and when the electric vehicle 15 participates in the V2G,the digital communication unit 102 performs an operation according to aninstruction indicated by the signal. The connection form between theexternal power supply 14 and the electric vehicle 15 is not limited tothe physical connection by the inlet 101 and the connector 22, and mayinclude electromagnetic connection such as non-contact charge/dischargein the state in which the inlet 101 and the connector 22 approach toeach other.

The bidirectional charger 103 converts an AC voltage obtained from theexternal power supply 14 via the inlet 101 and the digital communicationunit 102 into a DC voltage. By the power converted into the DC voltageby the bidirectional charger 103, the main battery 104 is charged.Furthermore, the bidirectional charger 103 converts a DC voltagedischarged from the main battery 104 into an AC voltage. The powerconverted into the AC voltage by the bidirectional charger 103 is sentto the external power supply 14 via the inlet 101. The main battery 104,for example, is a secondary battery that outputs a DC high voltage of100 V to 200 V, and supplies power to an electric motor (notillustrated) which is a driving source of the electric vehicle 15.

The converter 105 drops the output voltage of the main battery 104 to aconstant DC voltage. By the power dropped by the converter 105, thesub-battery 106 is charged. The sub-battery 106, for example, is asecondary battery that outputs a DC low voltage of 12 V, and suppliesthe power to an auxiliary machine and the like of the electric vehicle15.

The charge/discharge ECU 107, the battery ECU 108, and the radio unit109 surrounded by a dotted line of FIG. 2 start up or stop in accordancewith the instruction indicated by the signal received in the digitalcommunication unit 102 even when the electric vehicle 15 is beingparked. The charge/discharge ECU 107 controls an operation of thebidirectional charger 103. The charge/discharge ECU 107 controls theoperation of the bidirectional charger 103, so that the main battery 104is charged or discharged. The battery ECU 108 derives a remainingcapacity (SOC: State of Charge) of the main battery 104 and performscontrol relative to a power storage state and the like of the mainbattery 104.

The radio unit 109 wirelessly transmits, to the aggregator 17,information on participation or nonparticipation of the electric vehicle15 in the V2G, the degree of activeness in the case of participating inthe V2G, a time period in which participation in the V2G is possible, adischarge state of the main battery 104, and the like. The participationor nonparticipation in the V2G, the degree of activeness in the case ofparticipating in the V2G, and the time period, in which participation inthe V2G is possible, are set in advance by an owner of the electricvehicle 15. The owner of the electric vehicle 15 is assumed tounderstand that a discharge opportunity and a discharge amount of themain battery 104 are large as the degree of activeness of participationin the V2G is high.

FIG. 3 is a block diagram illustrating the aggregator 17 and thecommunication network 16 constituting a part of the V2G systemillustrated in FIG. 1. As illustrated in FIG. 3, the aggregator 17includes a power amount database 201, a setting information database202, an analysis unit 203, a decision unit 204, a transmission unit 205,and a radio unit 206.

The power amount database 201 is a database having past and currentinformation on a power amount supplied from the power supplier includingthe power station 11 to the power system and a power amount suppliedfrom the power system to the power consumer 13. The setting informationdatabase 202 is a database having information on the participation ornonparticipation of each electric vehicle 15 in the V2G, the degree ofactiveness in the case of participating in the V2G, and the time period,in which participation in the V2G is possible, the degree ofcontribution for the power system, and the like.

The analysis unit 203 performs time-series analysis of a power amount byusing the information of the power amount database 201, therebyperforming power demand/supply prediction in the power system. Thedecision unit 204 decides a time, at which discharge of the main battery104 of the electric vehicle 15 to the power system or charge of the mainbattery 104 by power supplied from the power system is performed, foreach electric vehicle 15 based on the power demand/supply predictionresult obtained by the analysis unit 203, information of each electricvehicle 15 stored in the setting information database 202, and the like.The transmission unit 205 transmits an instruction to the electricvehicle 15 via the communication network 16 and the external powersupply 14, wherein the instruction includes the time at which thedischarge or the charge of the main battery 104 is performed and thetime is decided by the decision unit 204. The decision unit 204 sets anincentive when performing the charge/discharge of the main battery 104of the electric vehicle 15 according to an instruction from theaggregator 17 to be higher than an incentive when performing the chargedischarge in other time periods. The incentive is a profit of an ownerof the electric vehicle 15 when the electric vehicle 15 sells and buyspower, and the profit is mainly money.

The radio unit 206 receives the information on the participation ornonparticipation in the V2G, the degree of activeness in the case ofparticipating in the V2G, the time period in which participation in theV2G is possible, the discharge state of the main battery 104, and thelike, which are wirelessly transmitted from the electric vehicle 15. Theinformation received in the radio unit 206 is stored in the settinginformation database 202.

Next, control of the charge/discharge of the main battery 104 of theelectric vehicle 15, which is managed by the aggregator 17, will bedescribed with reference to FIG. 4. When the connector 22 of theexternal power supply 14 is mounted at the inlet 101 of the electricvehicle 15, the digital communication unit 102 of the electric vehicle15 confirms whether it is possible to communicate with the aggregator 17via the external power supply 14 and the communication network 16 (stepS101). Next, the charge/discharge ECU 107, the battery ECU 108, and theradio unit 109 of the electric vehicle 15 stop operating (step S103).Next, when the digital communication unit 102 of the electric vehicle 15receives a signal including an instruction for discharge or charge ofthe main battery 104 from the aggregator 17 (step S105: Yes), theprocedure proceeds to step S107.

In step S107, the digital communication unit 102 determines whether thecurrent time is a timing earlier by a predetermined time to a start timeof the discharge or charge indicated by the instruction from theaggregator 17. When the current time is a time earlier by thepredetermined time, the procedure proceeds to step S109, and when thecurrent time is a time earlier by the predetermined time or more, theprocedure returns to step S105. When the signal reception time point instep S105 already exceeds the time earlier by the predetermined time tothe start time, the procedure proceeds to step S109 in order to preventfrequency occurrence of start-up and stop. In step S109, the digitalcommunication unit 102 starts to operate the charge/discharge ECU 107,the battery ECU 108, and the radio unit 109. Next, when the start timeis reached, the discharge or charge of the main battery 104 of theelectric vehicle 15 is started (step S111). Next, when an end timeindicated by an instruction received in advance from the aggregator 17is reached or when the digital communication unit 102 receives adischarge or charge end instruction from the aggregator 17 (step S113:Yes), the procedure returns to step S103, so that the charge/dischargeECU 107, the battery ECU 108, and the radio unit 109 of the electricvehicle 15 stop operating.

As described above, the charge/discharge ECU 107 starts the discharge ofthe main battery 104 at the discharge start time indicated by aninstruction from the aggregator 17, and ends the discharge of the mainbattery 104 at the discharge end time indicated by an instruction fromthe aggregator 17. However, when the SOC of the main battery 104 isequal to more than a predetermined value or the degree of activeness ofparticipation in the V2G is equal to more than a predetermined value,the charge/discharge ECU 107 may start the discharge from a time earlierto the start time indicated by the instruction from the aggregator 17,or end the discharge after the end time indicated by the instruction.For example, the discharge start time indicated by the instruction fromthe aggregator 17 is 18:00 and the end time is 19:00, thecharge/discharge ECU 107 may start the discharge of the main battery 104at 17:30 or end the discharge of the main battery 104 at 19:30. Asdescribed above, the aggregator 17 sets the degree of contribution forthe power system and an incentive to be high in the electric vehicle 15having the main battery 104 discharged longer than the instruction fromthe aggregator 17. Furthermore, in a power trading market in the V2G,there is an immediately previous adjustment market in which a unittrading time and a unit trading amount are small, separately from anormal trading market. When the main battery 104 can be dischargedlonger than the instruction from the aggregator 17, it is possible toperform power selling in the immediately previous adjustment market, sothat it is possible to further contribute to stabilization of the powersystem.

Next, the management of the aggregator 17 relative to thecharge/discharge of the main battery 104 of the electric vehicle 15 willbe described. FIG. 5 is a diagram illustrating each change in the outputand the SOC of the main battery 104 provided in the electric vehicle 15accompanied with an example of charge/discharge (including the V2G) ofthe main battery 104. In the example illustrated in FIG. 5, around 8:00in the morning, the electric vehicle 15, for example, runs from its ownhome to an office and then the main battery 104 is charged in theoffice. Then, the main battery 104 is left until about 6:00 p.m. and theelectric vehicle 15 runs from the office to its own home around 6:00p.m. When the electric vehicle 15 reaches its own home and is connectedto the external power supply 14, it can participate in the V2G. In theexample illustrated in FIG. 5, since a power demand amount rapidlyincreases for about 2 hours from about 6:00 p.m. at which the electricvehicle 15 returns to its own home and a power supply amount is smallerthan the power demand amount, a discharge instruction is sent from theaggregator 17 to the electric vehicle 15 connected to the external powersupply 14, so that the main battery 104 is continuously discharged.Thereafter, when the power demand is reduced, the main battery 104 ischarged and discharged in accordance with an instruction from theaggregator 17 until about 3:00 am. After 3:00 a.m., the main battery 104is fully charged for next morning running.

Within the V2G participation time period illustrated in FIG. 5, in atime period other than the continuous discharge, a charge/dischargeinstruction may be sent to the electric vehicle 15 in order to supplypower for adjusting a frequency in the power system to be stabilized.Even though no power is actually supplied to the power system, theaggregator 17 may set the degree of contribution for the power system tobe high in the electric vehicle 15 that contributes the stabilization ofthe frequency in the power system. Furthermore, when the external powersupply 14 communicable with the aggregator 17 is provided to an office,the V2G participation performed about 6:00 p.m. to about 3:00 a.m.illustrated in FIG. 5 may be performed in a daytime period asillustrated in FIG. 6 and FIG. 7. As with the example illustrated inFIG. 6 and FIG. 7, a stop state and a start-up state of thecharge/discharge ECU 107 and the like are switched for a vehicleactively participating in the V2G, so that it is possible to ensuredurability of these electric components.

FIG. 8 is a diagram illustrating a change in a demand and supply balanceof a power market and a temperature in the V2G participation time periodillustrated in FIG. 5 and a time period earlier to the V2G participationtime period. As illustrated in FIG. 8, in a power market of a day untilabout 5:00 p.m., since there is a margin in a power supply amount withrespect to a power demand amount, the aggregator 17 instructs theelectric vehicle 15, which can participate in the V2G, to charge themain battery 104 by power from the power system. However, since thepower supply amount is smaller than the power demand amount for abouttwo hours from about 6:00 p.m. of nightfall, the aggregator 17 instructsthe electric vehicle 15, which can participate in the V2G, to performdischarge of the main battery 104 to the power system. Thereafter, atnight, since there is also a margin in the power supply amount withrespect to the power demand amount, the aggregator 17 instructs theelectric vehicle 15, which can participate in the V2G, to charge themain battery 104 by power from the power system.

As described above, the aggregator 17 sends the discharge or chargeinstruction to the main battery 104 of the electric vehicle 15 which canparticipate in the V2G, wherein the instruction instructs a start timeand an end time of charge or discharge. The electric vehicle 15exchanges a power amount depending on a time from the start time to theend time with the power system. However, a power amount (Wh) per unittime, which is exchanged between the electric vehicle 15 and the powersystem, is smaller than a minimum trading unit (=a unit time×a unittrading amount) managed when the aggregator 17 exchanges power with thepower system. Therefore, the decision unit 204 of the aggregator 17decides a discharge time of each electric vehicle 15 such that adifference between a multiple of the minimum trading unit and a totalpower amount secured in the aggregator 17 for power selling to the powersystem can be compensated for by an amount of power discharged from themain battery 104 of each electric vehicle 15. In FIG. 8, the minimumtrading unit is expressed by a square shape and the total power amountsecured in the aggregator 17 for power selling to the power system isexpressed by a hatched area. The total power amount secured in theaggregator 17 for power selling to the power system includes an amountof power supplied from the power supplier including the power station11, in addition to an amount of power discharged from other electricvehicles.

Meanwhile, an amount of power, which can be reversely supplied (can besold) by one electric vehicle, is about 15 kWh to 50 kWh. On the otherhand, in the aforementioned minimum trading unit used in a power tradingmarket, for example, a value of 0.1 MWh (=1 hr×0.1 MW) to 1 MWh (=1 hr×1MW), which is not generally small at all, is set. Accordingly, it isdifficult to satisfy the minimum trading unit only by a single electricvehicle or a small number of electric vehicles. Therefore, inconsideration of the total power amount secured in the aggregator 17 forpower selling to the power system, setting discharge times of eachelectric vehicle is important to establish power trading including anagreement of power selling from the electric vehicle 15 to theaggregator 17.

When laws for an environmental car in each country such as a ZEV (ZeroEmission Vehicle) law in USA are enforced, an accelerated increase isexpected in the number of electric vehicles which can participate in theV2G in a company. Accordingly, the aggregator 17 designates dischargetimes of each electric vehicle, so that it is possible to easily satisfythe minimum trading unit and thus to rapidly increase power of eachelectric vehicle to be supplied to the power system.

Furthermore, based on the power demand/supply prediction result obtainedby the analysis unit 203, the degree of contribution of each electricvehicle 15 for the power system stored in the setting informationdatabase 202, and a charge appropriateness level of a charge time periodof the main battery 104 derived from the degree of deteriorationinfluence applied to the main battery 104, the decision unit 204 of theaggregator 17 decides a charge time of the electric vehicle 15 such thatthe main battery 104 is charged in a time period in which the chargeappropriateness level is high as the degree of contribution is high. Asa consequence, there are many cases where a charge start time in theelectric vehicle 15 with a high degree of contribution is a time periodin which the charge appropriateness level is high, so that it ispossible to delay progress of deterioration of the main battery 104 inthe electric vehicle 15 with a high degree of contribution.

The degree of deterioration influence applied to the main battery 104 isderived based on change prediction of a day's temperature in theposition of the electric vehicle 15. In general, when a temperature isexcessively high during charge of a secondary battery, the degree ofdeterioration influence becomes high. In the example illustrated in FIG.8, in a time period just shifted to night from nightfall, since atemperature is still high and the degree of deterioration influence ishigh, the charge appropriateness level is low. However, in a midnighttime period, when the temperature falls and for example, reaches about25° C. since the degree of deterioration influence becomes low, thecharge appropriateness level becomes high.

In contrast, in a cold region, the temperature excessively falls in amidnight time period. When the temperature at the time of charge falls,since there occurs a precipitation phenomenon of an active material in anegative electrode which is called electrodeposition, it is necessary tolimit a charging current in consideration of deterioration of durabilityfor the charge/discharge of the main battery 104. Furthermore, in ageneral lithium ion battery, when the temperature at the time of chargefalls, since the activity of a chemical reaction in the main battery 104falls, a long time is required for the charge of the main battery 104 byconstant voltage charge. Due to these factors, since a long time isrequired for the full charge of the main battery 104, a long time isalso required to use electric components depending on charge. As aconsequence, since the usage deterioration of the electric components isalso promoted, the charge appropriateness level is low in the midnighttime period of the cold region. On the other hand, in the case of thetime period just shifted to night from nightfall, since the temperatureis higher than that of the midnight time period, it is not necessary tolimit the charging current. Furthermore, since a long time is notrequired for the full charge of the main battery 104, the chargeappropriateness level is higher than that of the midnight time period.

Furthermore, the aggregator 17 sets the degree of contribution for thepower system and an incentive to be high in the electric vehicle 15having the main battery 104 discharged longer than the discharge timedecided by the decision unit 204. For example, when the start time ofthe discharge time decided by the decision unit 204 is 18:00 and the endtime is 19:00, the aggregator 17 sets the degree of contribution to behigh in the electric vehicle 15 of the main battery 104 discharged from17:30 to 19:00 or the electric vehicle 15 of the main battery 104discharged from 18:00 to 19:30.

As described above, according to the present embodiment, thecharge/discharge time of the main battery 104 of the electric vehicle 15participating in the V2G is decided by the aggregator 17 based on thepower demand/supply prediction result and the like in the power system.Therefore, in the time period in which the power supply amount issmaller than the power demand amount, when power is supplied from theelectric vehicle 15 to the power system according to an instruction fromthe aggregator 17, the stability of supply of power to the powerconsumer 13 from the power system is improved. In the time period inwhich there is a margin in the power supply amount with respect to thepower demand amount, when the main battery 104 of the electric vehicle15 is charged, the stability of the power system is improved.Furthermore, an incentive of an owner of the electric vehicle 15 in thecase of performing charge/discharge according to an instruction from theaggregator 17 is set to be high, resulting in an increase in a profitratio of the owner of the electric vehicle 15 when performing the V2G.Moreover, the charge/discharge time of the main battery 104 of theelectric vehicle 15 is decided by the aggregator 17 based on the minimumtrading unit of a power amount managed when exchanging power with thepower system. Thus, it is possible to improve the probability of anagreement of power selling from the electric vehicle 15 to theaggregator 17 and the probability of power selling from the aggregator17 to the power system. By such advantages, it is possible to promoteactive participation of the electric vehicle 15 in the V2G, so that thestability of the power system is also achieved. As described above,according to the present embodiment, it is possible to maximize a profitof four parts of the aggregator 17, an owner of the electric vehicle 15,a person running the power system, and the power consumer 13, which areinvolved in the V2G. Moreover, since the charge/discharge ECU 107, thebattery ECU 108, and the radio unit 109 of the electric vehicle 15 donot operate except for the charge/discharge time according to aninstruction from the aggregator 17 and a standby time thereof, it ispossible to ensure durability of these elements which can stop.Furthermore, it is possible to reduce power consumption by theseelements which can stop.

Furthermore, the aggregator 17 decides a discharge time of each electricvehicle 15 such that a difference between a multiple of the minimumtrading unit, which is used in a power trading market and is notgenerally small at all, and a total power amount secured in theaggregator 17 for power selling to the power system can be compensatedfor by an amount of power discharged from the main battery 104 of eachelectric vehicle 15. The main battery 104 of the electric vehicle 15 hasdifficulty in accumulating large power to the extent that the minimumtrading unit is satisfied and discharge of large power is not requiredfor the electric vehicle 15, but since the aforementioned difference issmaller than the minimum trading unit, the agreement probability ofpower selling from the electric vehicle 15 to the aggregator 17 isimproved. Furthermore, the aggregator 17 can maximally perform powerselling to the power system.

Furthermore, based on the degree of contribution for the power systemand the charge appropriateness level, the aggregator 17 decides thecharge time of the electric vehicle 15 such that the main battery 104 ischarged in the time period in which the charge appropriateness level ishigh as the degree of contribution is high. Since there are many caseswhere charge start is instructed in the time period in which thetemperature is low with respect to the electric vehicle 15 with a highdegree of contribution, it is possible to delay progress ofdeterioration of the main battery 104. Particularly, in the time periodin which the charge appropriateness level is high, it is possible toallow the progress of deterioration of the main battery 104 to beapproximately zero. By such advantages, it is possible to promote activeparticipation of the electric vehicle 15 in the V2G with respect to anowner of the electric vehicle 15 who hesitates participation in the V2Gdue to anxiety such as deterioration of the electricity storage unitwhen participating in the V2G.

Furthermore, when the SOC of the main battery 104 is equal to more thana predetermined value or the degree of activeness of participation inthe V2G is equal to more than a predetermined value, the aggregator 17sets the degree of contribution for the power system and an incentive tobe high in the electric vehicle 15 having the main battery 104discharged longer than an instruction from the aggregator 17.Consequently, a profit ratio of an owner of the electric vehicle 15 whenperforming the V2G becomes high, so that it is possible to promoteactive participation of the electric vehicle 15 in the V2G. Furthermore,in the case of discharge in the time period in which the power supplyamount is smaller than the power demand amount, the stability of thepower system is improved. Furthermore, in a power trading market in theV2G, there is an immediately previous adjustment market in which theunit trading time and the unit trading amount are small, separately froma normal trading market, and when the main battery 104 can be dischargedlonger than the instruction from the aggregator 17, the electric vehicle15 can perform power selling in the immediately previous adjustmentmarket, so that it is possible to further contribute to thestabilization of the power system. As described above, it is possible tomaximize a profit of four parts of the aggregator 17, an owner of theelectric vehicle 15, a person running the power system, and the powerconsumer 13, which are involved in the V2G.

Note that the present invention is not limited to the aforementionedembodiment and modification, improvement and the like can beappropriately made. For example, the bidirectional charger 103 and thecharge/discharge ECU 107 of the electric vehicle 15 may be provided tothe external power supply 14. In this case, power exchange between theelectric vehicle 15 and the external power supply 14 is performed by adirect current. Furthermore, the battery ECU 108 and the radio unit 109of the electric vehicle 15 start up or stop in accordance with aninstruction indicated by a signal received in the digital communicationunit 102 even when the electric vehicle 15 is being parked.

DESCRIPTION OF REFERENCE NUMERALS AND CHARACTERS

-   -   11 power station    -   12 power transmission network    -   13 power consumer    -   14 external power supply    -   15 electric vehicle    -   16 communication network    -   17 aggregator    -   18 home gateway    -   21 cable    -   22 connector    -   23 digital communication unit    -   101 inlet    -   102 digital communication unit    -   103 bidirectional charger    -   104 main battery    -   105 converter    -   106 sub-battery    -   107 charge/discharge ECU    -   108 battery ECU    -   109 radio unit    -   201 power amount database    -   202 setting information database    -   203 analysis unit    -   204: decision unit    -   205 transmission unit    -   206 radio unit

1. A V2G system comprising: a power system; a charging/dischargingdevice including an electricity storage unit that is provided in atransport equipment, a power conversion unit that converts powertransferred between the electricity storage unit and the power system, areception unit that receives a signal from an external device, and acontrol unit that controls an operation of the power conversion unitbased on the signal received by the reception unit; and a server devicethat manages charging and discharging of the electricity storage unit inthe charging/discharging device, wherein the server device performs atime-series analysis on an amount of power supplied from a powersupplier to the power system and an amount of power supplied from thepower system to a power consumer, determines a period of time duringwhich power is discharged from the electricity storage unit of thecharging/discharging device to the power system or during which theelectricity storage unit is charged using power supplied from the powersystem based on a result of estimating a power supply-demand state ofthe power system and a minimum trading unit of an amount of powermanaged by the server device during power transfer with the powersystem, and transmits an instruction including the period of time duringwhich the discharging or the charging is performed to thecharging/discharging device, and the control unit of thecharging/discharging device starts up or stops based on the period oftime indicated by the instruction that is transmitted from the serverdevice and is received by the reception unit.
 2. The V2G systemaccording to claim 1, wherein the server device determines a period oftime during which the discharging of the charging/discharging device isperformed based on the result of estimating the power supply-demandstate, the minimum trading unit of the amount of power managed duringpower transfer with the power system, and a total amount of powersecured for selling to the power system.
 3. The V2G system according toclaim 1, wherein the server device determines a period of time duringwhich the charging of the charging/discharging device is performed basedon the result of estimating the power supply-demand state, a degree ofcontribution of the charging/discharging device to the power system, anda charge appropriateness level of a time slot in which the electricitystorage unit is charged such that, as the degree of contributionincreases, the electricity storage unit is charged in a time slot havinga higher charge appropriateness level, the charge appropriateness levelbeing calculated from an influence on deterioration of the electricitystorage unit.
 4. The V2G system according to claim 1, wherein in a casewhere an amount of power stored in the electricity storage unit is apredetermined amount or higher, the control unit of thecharging/discharging device controls an operation of the powerconversion unit such that the discharging starts at a time, which isearlier by a predetermined period of time than a start time of thedischarging indicated by the instruction, and is performed until an endtime of the discharging indicated by the instruction, and the serverdevice manages a degree of contribution of each of thecharging/discharging devices to the power system and sets thecontribution to be high for the charging/discharging device includingthe electricity storage unit which performs the discharging for a periodof time longer than the period of time during which the discharging isperformed indicated by the instruction.
 5. The V2G system according toclaim 1, wherein in a case where a preset activeness of discharging fromthe electricity storage unit to the power system is a predeterminedvalue or higher, the control unit controls an operation of the powerconversion unit such that the discharging starts at a time, which isearlier by a predetermined period of time than a start time of thedischarging indicated by the instruction, and is performed until an endtime of the discharging indicated by the instruction, and the serverdevice manages a degree of contribution of each of thecharging/discharging devices to the power system and sets thecontribution to be high for the charging/discharging device includingthe electricity storage unit which performs the discharging for a periodof time longer than the period of time during which the discharging isperformed indicated by the instruction.
 6. The V2G system according toclaim 1, wherein in a case where an amount of power stored in theelectricity storage unit is a predetermined amount or higher, thecontrol unit controls an operation of the power conversion unit suchthat the discharging starts at a start time of the discharging indicatedby the instruction and is performed until a time which is later by apredetermined period of time than an end time of the dischargingindicated by the instruction, and the server device manages a degree ofcontribution of each of the charging/discharging devices to the powersystem and sets the contribution to be high for the charging/dischargingdevice including the electricity storage unit which performs thedischarging for a period of time longer than the period of time duringwhich the discharging is performed indicated by the instruction.
 7. TheV2G system according to claim 1, wherein in a case where a presetactiveness of discharging from the electricity storage unit to the powersystem is a predetermined value or higher, the control unit of thecharging/discharging device controls an operation of the powerconversion unit such that the discharging starts at a start time of thedischarging indicated by the instruction and is performed until a timewhich is later by a predetermined period of time than an end time of thedischarging indicated by the instruction, and the server device managesa degree of contribution of each of the charging/discharging devices tothe power system and sets the contribution to be high for thecharging/discharging device including the electricity storage unit whichperforms the discharging for a period of time longer than the period oftime during which the discharging is performed indicated by theinstruction.
 8. A method of charging and discharging an electricitystorage unit in a V2G system, the V2G system including a power system, acharging/discharging device, and a server device, thecharging/discharging device including the electricity storage unit thatis provided in a transport equipment, a power conversion unit thatconverts power transferred between the electricity storage unit and thepower system, a reception unit that receives a signal from an externaldevice, and a control unit that controls an operation of the powerconversion unit based on the signal received by the reception unit, theserver device managing charging and discharging of the electricitystorage unit in the charging/discharging device, and the methodcomprising: causing the server device to perform a time-series analysison an amount of power supplied from a power supplier to the power systemand an amount of power supplied from the power system to a powerconsumer, to determine a period of time during which power is dischargedfrom the electricity storage unit of the charging/discharging device tothe power system or during which the electricity storage unit is chargedusing power supplied from the power system based on a result ofestimating a power supply-demand state of the power system and a minimumtrading unit of an amount of power managed by the server device duringpower transfer with the power system, and to transmit an instructionincluding the period of time during which the discharging or thecharging is performed to the charging/discharging device; and causingthe control unit of the charging/discharging device to start up or stopbased on the period of time indicated by the instruction that istransmitted from the server device and is received by the receptionunit.